01 -
Preheat oven to 350°F (175°C) and grease a 9x13-inch baking pan.
02 -
Whisk flour, brown sugar, granulated sugar, kosher salt, cinnamon, and pumpkin pie spice in a large bowl. Pour melted butter over dry ingredients and mix until large moist crumbs form. Reserve streusel.
03 -
In another large bowl, whisk together flour, granulated sugar, baking powder, baking soda, kosher salt, pumpkin pie spice, and cinnamon.
04 -
Add softened butter cubes and half of the pumpkin puree to dry mixture. Beat on medium speed until a stiff dough forms.
05 -
In a separate bowl, whisk the remaining pumpkin puree, eggs, vegetable oil, and vanilla extract until fully combined.
06 -
Gradually add pumpkin-egg mixture to dough in three additions, mixing for 20 seconds after each, then beat for 1 minute until light and fluffy.
07 -
Spread 2 cups of cake batter into prepared pan. Sprinkle 1 cup of streusel over batter. Repeat with 2 more cups batter, 1 cup streusel, then remaining batter, followed by 2 cups streusel.
08 -
Bake for 35 minutes. Remove pan and quickly sprinkle remaining streusel evenly over surface.
09 -
Return cake to oven and bake 10–15 minutes, or until a toothpick inserted in the center comes out clean.
10 -
Allow cake to cool in the pan on a wire rack for 15–20 minutes.
11 -
Beat softened butter until smooth. Add vanilla extract, kosher salt, milk, and powdered sugar. Beat until silky, adding additional milk if needed for drizzling consistency.
12 -
Drizzle icing over warm cake and serve.